Silicon-resin foams



Patented Aug. 28, 1951 SILICON-RESIN FOAMS John B. Rust, East Hanover,and Leonard Spialter, Newark, N. J., assignors, by direct and mesneassignments, of one-half to Montclair Research Corporation, acorporation of New Jersey, and one-half to Ellis-Foster Company, acorporation of New Jersey No Drawing. Application March 3, 1947, SerialNo. 732,134

11 Claims.

This invention relates to silicon-resin foams, that is, to resin-formingorgano-silicon compounds which have been converted into foams such asfoamed silicones, to methods of making such products and to theirutilization.

Among the objects of the present invention is the preparation ofsilicon-resin foams such as foamed silicones and related products.

Further objects include methods of producing such foams.

Still further objects and advantages of the present invention willappear from the more detailed description set forth below, it beingunderstood that such more detailed description is given by way ofillustration and explanation only, and not by way of limitation, sincevarious changes therein may be made by those skilled in the art withoutdeparting from the scope and spirit of the present invention.

In accordance with the present invention resin-forming organo-siliconderivatives either as compounds per se, or mixtures or compositionscontaining them, are converted into solid foams. Any resin-formingorgano-silicon derivative which is capable of passing through a liquidstage in which it may be caused to produce a froth and then cured toform a solid foam may be utilized. The organo-silicon derivativescapable of being utilized in this way are generally those which containhydrocarbon or substituted hydrocarbon groups attached to the silicon aswell as oxygen attached to the silicon and they may be generallyreferred to as resin-forming organo-silicone compounds or mixturesor-compositions containing them. Other terms may be utilized indescribing such derivatives are orr gano-siloxanes, silicone polymers,or organosilicon oxides. The character of foam produced depends on theaverage length and character of the organo groups attached to thesilicon and on the ratio of such organo groups to silicon. For example,where alkyl groups are present the resin-forming organo-siliconecompound will be one which contains an average of 0.5 to 2 alkyl groupsper silicon atom in the silicon portion of the composition and theaverage length and character of the alkyl groups as well as the alkyl tosilicon ratio will determine the characteristics of the ultimate foamobtained. For example, higher alkyl groups and ratios of alkyl group tosilicon approaching 2 give resilient rubbery foams which may be utilizedfor example, for fillers, packing, shock absorbers, and the like.Conversely, the lower alkyl groups and ratios of such groups to siliconapproaching 0.5 yield hard 2 inflexible foams particularly adapted forinsulation purposes, supports, etc. Thus it is possible to control thecharacteristics of the foams obtained by the nature of the groupspresent and the ratio of such organo groups to silicon and variation inthe characteristics and properties of the foams may be made by choice ofsuch substituent groups and the ratios in which they are employed.

Such resin-forming organo-silicon compounds include the hydrolysisproducts of organo-silicon halides, silicon esters, silicon acylates,alkoxy silicons, substituted alkoxy silicons such as chloroalkoxysilicons obtained for example, by reaction of silicon halides such aschloro silicons with olefine oxides such as ethylene oxide and propyleneoxide, the esters and acylates already mentioned such as siliconacetates, etc., and various condensation products and mixtures of suchproducts obtained as the result of the action of water, heat, chemicalagents, and the like.

Organo-silicon halides include particularly those halides which containchlorine and bromine and are capable of being hydrolyzed to produceresin-forming materials. Such halides will generally contain 2 or 3halogens attached to the silicon and various mixtures of suchorganosilicon halides may be employed including also the organo-siliconmonohalides and various combinations of them with the halides mentionedabove. Individual organo-silicon halides as set forth above may behydrolyzed and used to produce resin-forming materials or variousmixtures of the various organo-silicon halides may be employed andcohydrolysis products produced from them in the production ofresinforming materials, or mixtures of hydrolyzed organo-silicon halidesmay be employed.

While the halides particularly referred to have been indicated aschlorides and bromides, the fluorine derivatives may also be employed,particularly the halides containing 3 fluorine atoms attached to siliconwhich on hydrolysis yield silicone types of products where fluorine isstill retained in the molecule attached to silicon. Mixtures of suchsilicon fluorides with other halides such as the chlorides and bromidesmay also be employed to produce complex products in which some fluorineis retained in the molecule to modify the characteristics of. theultimate product obtained. In such organo-silicon halides and in thealkoxy silicons that are utilized, the organo groups may includealiphatic radicals both saturated and unsaturated such as the alkylsincluding methyl, ethyl, propyl, isopropyl,

butyl, isobutyl, the various amyls, hexyl, heptyl, octyl, etc., up tothe higher alkyl groups such as those containing from '16 to 18 and 20carbon atoms, etc., as well as the unsaturated aliphatics including theoleflnyl derivatives such as vinyl, allyl, etc.; or the organo groupsmay be carbocyclic including phenyl, tolyl, etc., or alkaryl and aralkylsuch as benzyl; or the organo groups may be cycloaliphatic includingsuch groups as cyclohexyl, or they may be naphthenic; or various mixedorgano substituents may be present in the silicon derivatives. Thesilicon esters and acylates may be those produced from aliphatic acidsincluding the fatty acids such as acetic acid, etc., or aromatic acidsand esters of both monobasic and polybasic acids may be included. It isnot necessary to utilize individual compounds as the resin-formingorgano-silicon derivatives, but mixtures of any of the statedderivatives as set forth above may be utilized.

The organo-silicon derivative employed should be one which isresin-forming and desirably should pass through a viscous liquid stagein which stage the material may be heated to cause it to froth so thatthe froth may be cured to produce a solid foam. The temperatures of theheat treatment of the organo-silicon derivatives to produce the foamwill necessarily vary with the type of material and compositions andmixtures undergoing treatment. Ordinarily the temperature will be atleast 100 C. which may be suitable for some of the methyl silicones oflow methyl-to-silicon ratio, but generally the lower limit oftemperature employed will be about 200 to 250 C., while the uppertemperature range will run up substantially to the order of about 500 to550 C., again depending on the nature of the products undergoingtreatment and the conditions under which the treatment is carried out.Some materials like n-butyltriacetoxysilane may not foam appreciably attemperatures of the order to 360 C. but will produce very satisfactoryfoams at temperatures of 440 C. So that the range of temperaturesemployed necessarily depends on the nature of the material undergoingtreatment. Ordinarily the temperature which is used for such foaming andcuring operation will be at least 40 to above the temperaturesordinarily utilized for producing curing of the organo-siliconderivative as a film in the production of surface coatings. In manycases the temperatures will be 100 to 200 C. above such curingtemperatures and such higher temperatures may be utilized to give thenecessary heating to produce the foaming and curing operation. Thelength of time treatment necessary for producing such foaming and curingagain depends on the nature of the materials under-.

going treatment and the temperatures at which the operations are carriedout and will be determined by the product being .sought. Foaming andcuring need not be carried out in a single operation but the heattreatment to produce foaming may be carried out followed by a heattreatment to produce curing either at the same or a differenttemperature from that at which the foaming has been carried out.

Various modifications of the methods of producing foams as set forthabove, may be used. For example, gases or vapors may be bubbled throughthe resins while in liquid condition at the foaming stage just beforecuring. Gases inert to the resin, such as nitrogen, are preferred unlesssome special effect is to be sought due to action of the gaseous orvaporous material. An-

other expedient that may be used is to add to the resins, before thecuring stage, compounds which liberate gases at the temperatures used,to assist foaming. Further, subor super-atmospheric pressures may beutilized in some cases. For example, heating a silicone of the characterset forth above, under pressure to just before curing and then releasingthe pressure or applying vacuum or suction will cause the resin to yielda very porous solid foam of low density. Any combination of thesetechniques may be employed. They are not necessary since, as explainedhereinabove, the simple heat treatment will produce foamed silicones,but they may be employed for special effects. The proportions ofcompounds used are not critical. The only requirement is that in thesilicone itself, before the curing stage, the ratio of alkyl to siliconbe from 0.5 to 2, the limits of curing silicon resins. For example, inExample 14, the ratio is about 1.3 to 1. The types of starting materialsare not critical either as long as they can be made-to form siliconeresins, by any technique, with the desired alkylto-silicon ratios forcuring resins. Non-reacting silicon compounds such as the tetra-alkylsilanes may'be present as plasticizers, lubricants, etc.; but since theydo not enter into the silicone resin structure, they do not affect theratio.

The foams produced in accordance with the present invention exhibit goodmoisture-, heat-, and chemical resistance, low electrical conductivityand many other desirable electrical properties. Their utilizationdepends on the particular types of materials that it has been sought toproduce and as indicated above resilient rubbery products may beproduced suitable for use as fillers, packing, shock absorbers, and thelike, whereas, hard inflexible foams may be produced particularlyadapted for insulation purposes, as for example, heat insulation, soundinsulation, electrical insulation, etc., or such hard inflexible foamsmay be used as supports, etc. Foams of the present invention may be usedin buoyancy apparatus such as floats, rafts, buoys, and so forth. Thesolid silicon foams may be fabricated into various shapes either byforming them in molds, or by cutting, machining, grinding, or otheroperations on the block form of material.

Example 1.A mixture of 0.78 g. (0.005 mole) diethyldichlorosilane and2.88 g. (0.015 mole) nbutyltrichlorosilane was dissolved in 25 cc. etherand hydrolyzed by dropping on cracked ice. The ether layer was placed ina small beaker fitted with a stirrer and warmed to eyaporate off theether. The residue of mixed silicols was then heated with stirring at C.for 1 hours to condense the material to. a viscous liquid. To the cooledviscous liquid was stirred in first 2 g. (0.01 mole) ethyl orthosilicateand then 1 drop concentrated hydrochloric acid. Reheating at 195 C. for20 minutes caused frothing of the material and curing of the froth intoa stable solid foamed silicone resin.

Example 2.-About 5 g. of n-butyl trichlorosilane was dissolved in 50 cc.anhydrous ether and hydrolyzed by pouring on cracked ice. The etherlayer of silicol was separated, dried over anhydrous sodium sulfate andplaced in a large Pyrex test tube. The ether was evaporated off withentle heat to leave a residue of the fluid silicol. This was then heated15 minutes at 250 C. to bring about intermolecular condensation to aviscous resin with the elimination of water. Further heating for 30minutes at 360 C. caused a vigorous frothing and subsequent curing to alight, colorless, porous, resilient foam, more than five times as largein volume as the original liquid.

Example 3.About 5 g. of hydroyzed phenyldichlorosilane was placed in alarge Pyrex test tube and heated five minutes at 360 C. (by immersion ina hot salt bath). The liquid was converted completely to a foam. Curing15 minutes more at 360 C. gave a colorless highly porous tough mass.

Example 4.Two parts each of hydrolyzed phenyl-dichlorosilane andhydrolyzed diphenylchlorosilane were mixed together and heated at245-250 C. for 4 /2 hours while air was slowly bubbled through. Theviscous liquid obtained was then heated 2 minutes at 370 C. to convertit to a large mass of froth which after one more hour at 370 C. curedand set to a bulky, clear. light-yellow strong solid foam.

Example 5.-Five grams of the cohydrolysis product of two moles ofdimethyl chlorosilane and one mole of n-butyltrichlorosilane was placedin a large Pyrex test'tube. Through a capillary tube, a fine stream ofair bubbles was led through the mixture while it was being heated at 160C. for 3 hours and then 190 C. for 2- hours. The material was near itsgelation point. It was then foamed and cured at.370 C. for minutes toyield a porous spongy, rubbery, colorless mass of less than one-tenththe density of the Original liquid.

Example 6.--A sample of hydrolyzed n-butyldichlorosilane was heated for1 hour at 370 C. The material, still liquid, was cooled to roomtemperature and 25% of its volume of ethyl orthosilicate was added. Themixture was then heated at 370 C. for 1 hours to give a dark poroussticky silicone sponge.

Example 7.Puri1ied nitrogen gas was rapidly bubbled through a sample ofn-butyltriacetoxysilane being heated at 440 C. The gas bubbles stirredthe material and maintained an atmosphere of nitrogen above it. Aceticanhydride distilled off during the first few minutes as the compoundcondensed. Treatment for minutes more at this temperature yielded a softporous spongy product having little odor.

Example 8.--A sample of hydrolyzed benzyldichlorosilane was heated at440 C. while a stream of purified nitrogen gas was bubbled in. After 45minutes, there was obtained a hard, brittle, solid foam.

Example 9.--Repeating Example 8, but without employing the nitrogen gas,a foamed silicone was obtained in 15 minutes at 440 C.

'Example 10.A solution was made of two volumes of n-butyltriacetoxysilane to one volume of tetrakis (beta chloropropoxy) silane.It was heated under reflux for minutes at 420 C. During the initialheating, the material refluxed vigorously and slowly thickened. It thenfrothed completely and cured to a hard brittle foam.

' Example 11.-The Dow-Corning silicone resin #2052 with a 55.8% solidscontent, a viscosity 01.

3.45 poises at C., lot No. V-3, and a filmcuring time of 4 hours at 200C. was used. A sample was heated to evaporate oil the solvent, and wasthen heated in a molten salt bath at 360 C. for 10 minutes to yield, oncooling, a slightly tacky porous resilient spongy product.

Example 12.-A sample of the resin #2052 of Example 11, after removal ofthe solvent, was heated at 250 C. to give, on cooling, a tacky porousproduct.

Example 13.-A sample of Dow-Corning sili- 6 cone resin #801, with a70.0% solids content by weight, a viscosity of 5.4 poises at 25 0., lotNo. A-211, and a film-curing time of less than one hour at 250 C. washeated to remove the solvent. It was then subjected over a period of 45minutes to heat at a slowly rising temperature from 275-325 C. Foamingand curing occurred. The product on cooling to room temperature was atough, rubbery porous mass.

Example 14.A 'dioxane solution of- 4 moles diethyl dichlorosilane, lmole of tetra-acetoxysilane, and 1 mole of condensed ethyl silicate(commercial product of Union Carbide and Carbon Chemicals Corporation)was hydrolyzed with water to yield a cloudy solution of silicone. Thesilicone was extracted with ether repeatedly and the solvent was thenremoved by heat at 160 C. for 10 minutes. The alkyl to silicon ratio wasabout 1.3:1.

A sample of the silicone obtained was heated for 5 minutes at 330 C. tocause it to foam to more than ten times its original volume, and tocure. On cooling, to room temperature, there was obtained a strong,colorless, rigid, uniformly porous solid foam.

Another sample of the silicone was heated at 160 C. for 2 hours to forma weak gel. Heating this product for 4 minutes at 370 C. then yielded avery strong, colorless, firm solid foam.

Example 15.--Substituting diethyl diacetoxy silane for the diethyldichlorosilane, tetra-propionoxysilane for the tetra-acetoxysilane, andpolyethyl silicate (also a commercial product of Union Carbide andCarbon) for the condensed ethyl silicate, in Example 14, analogousresults were obtained, but the solid foams obtained were slightly harderand darker in color.

Having thus set forth our invention, we claim:

1. The method of producing an organo silicon oxide froth which comprisesfrothing by heating in liquid condition at a froth-producing temperatureof at least 100 C., in the absence of any added froth-producing agent, aliquefiable resinforming organo silicone capable of frothing in theabsence of any added frothing agent while in the liquid state atelevated temperature and capable of being transformed to the solid stateby heat alone, the organo groups being monovalent hydrocarbon radicals,the ratio of hydrocarbon groups to silicon being an average of from 0.5to less than 2 per silicon atom, said silicone being the only reactantpresent, and transforming the liquid froth to solid state by heat alone.

2. The method of claim 1 in which the silicone is halogen-hydrolyzedorgano silicon halide, the organo groups being monovalent hydrocarbonradicals.

3. The method of claim 1 in which the silicone is halogen-hydrolyzedaryl substituted silicon halide.

4. The method of claim 3 in which the silicon halide is phenyldichlorosilane, and the frothing temperature is about 360 C.

5. The method of claim 3 in which the silicon halide includes 'phenyldichlorosilane and diphenyl chlorosilane and the frothing temperature isabout 370.

6. The method of claim 1 in which the silicone is halogen-hydrolyzedorgano silicon halide, the organo groups being monovalent hydrocarbonradicals the halide having hydrogen attached to silicon.

7. The method of claim 1 in which the silicone is halogen-hydrolyzed'alkyl substituted silicon REFERENCES CITED halide.

a. The method of claim 7 in which the halide i g g i ffi are rem! isn-butyl silicon tri-chlorlde. 9. The method 01 claim 7 in which thehalide 5 UNITED STATES PATENTS 1s n-butyl dichlorosilane. Number NameDate 10. The method of claim 1 in which the Silicone V 2,386,995 WigalOct. 16, 1945 is halogen-hydrolyzed dimethyl chlorosilane co- 2,410,737Jenny Nov. 5, 1946 hydrolyzed with halogen-hydrolyzed n-butyl tri-2,441,422 Krieble et a1. May 11, 1948 chlorosilane. 7 10 2,441,423Elliot et a1. May 11, 1948 11. The method of claim 1 in which the Sili oe 2,448,556 Sprung Sept. 7, 1948 is halogen-hydrolyzed benzyldi-chlorosil ne. 2,460,795 Warrick eb. 1,194

JOHN B. RUST. LEONARD SPIALTER'.

1. THE METHOD OF PRODUCING AN ORGANO SILICON OXIDE FROTH WHICH COMPRISESFROTHING BY HEATING IN LIQUID CONDITION AT A FROTH-PRODUCING TEMPERATUREOF AT LEAST 100* C., IN THE ABSENCE OF ANY ADDED FROTH-PRODUCING AGENT,A LIQUEFIABLE RESINFORMING ORGANO SILICONE CAPABLE OF FROTHING IN THEABSENCE OF ANY ADDED FROTHING AGENT WHILE IN THE THE LIQUID STATE ATELEVATED TEMPERATURE AND CAPABLE OF BEING TRANSFORMED TO THE SOLID STATEBY HEAT ALONE, THE ORGANO GROUPS BEING MONOVALENT HYDROCARBON RADICALS,THE RATIO OF HYDROCARBON GROUPS TO SILICON BEING AN AVERAGE OF FROM 0.5TO LESS THAN 2 PER SILICON ATOM, SAID SILICONE BEING THE ONLY REACTANTPRESENT, AND TRANSFORMING THE LIQUID FROTH TO SOLID STATE BY HEAT ALONE.